1. Field of the Invention
The present invention relates to a high-strength, high-toughness, weldable and deformable rare earth magnesium alloy.
2. Description of the Related Art
Comparing with the mature industries of steel, aluminum, copper and the like, the proportion of deformable magnesium alloy in magnesium alloy industry is too low, only less than 10%, due to the following reasons: a) the technology of the magnesium alloy industry is still immature; b) the magnesium industry still has a very large technology space and a profit space.
In deformable magnesium alloys, the common alloy series are Mg—Mn, Mg—Al and Mg—Zn—Zr series. Trademark MB1, namely, Mg—Mn binary alloy, has a good corrosion resisting property; however, its strength is not high. MB8 developed for overcoming the drawback thereof comprises rare earth cerium which has the function of fining crystal grains and increasing strength. The strength of an alloy can be increased again by further increasing the content of Ce, and therefore, MB14 was developed as well. MB2, namely, AZ31 of US, belongs to Mg—Al series and is a deformable alloy with a wide application. The subsequent MB3 to MB7 are all developed on the basis of MB2 and comprise more Al or Zn. Although the strengths of MB3 to MB7 are increased, the plastic properties decreased largely, and the present research indicates that appropriate amount of rare earths can increase the overall performance. Corresponding to ZK60 of US, MB15 belongs to Mg—Zn—Zr series and is a high-strength alloy which can be age strengthened. The content of Zr is relatively stable, generally 0.6˜0.8%, however, when Zn excesses 4.5%, the plastic property will decrease largely. In order to obtain the overall performance, MB21 is adopted in China (the content of Zn is low). In this way, Mg—Zn—Zr series is separated into the two types of high zinc alloys and low zinc alloys, wherein MB21, MB22 belong to low zinc alloys, while MB15, MB25 belong to high zinc alloy. MB25 further comprises rare earth Y as compared with MB 15.
From what described above, it can be seen that addition of rare earths on the basis of primary alloy series is an effective way for increasing performance, and the rare earths are also necessary ingredients for achieving a good high temperature resistance performance. However, by various strengthening manner, the performance of Mg—Zn—Zr series excels the other two series.
It is well known that magnesium alloy is a light metal material and the rare earth elements have specific effects in the aspects of improving the strength, heat resistance and the like of the traditional magnesium alloys. However, the addition of rare earths, for example, Nd, Y, La, is always performed in a manner of a single pure rare earth in many scientific research departments and producing factories except that Ce is always added in a manner of cerium-rich mixed rare earth.